Decorative aluminum article and method for making the same



July 10, 1962 E. H. HOLLINGSVVORTH EI'AL 3,043,754

DECORATIVE ALUMINUM ARTICLE AND METHOD FOR MAKING THE SAME Filed Dec. 3, 1959 INVENTORS [rnesf H. lfollingswori)? a fled lie/1Q! This invention relates to aluminum articles, and more particularly to imparting a decorative pattern of a permanent nature to surfaces of aluminum articles.

The most commonly employed methods for casting ingots of aluminum and aluminum alloys involve the use of closed bottom heavy walled ferrous metal molds or open ended thin walled molds or dies. In the continuous casting process the molten metal is poured into a short open-ended mold which is drastically chilled by a stream of coolant and in many cases the emerging cast product is also chilled by the direct application of Water either as a run-01f from the mold or as a water spray. The closed bottom molds of the tilting type which have been commonly used are pivoted adjacent the top so that the molds turn about the pivot as the molds are raised or lowered. Pouring of the molten metal is started when the mold is in a raised or nearly horizontal position and is continued as the mold is lowered to a vertical, position. To facilitate extraction of the ingots from the molds, the latter are usually made in two vertical sections which are hinged on one side and releasably clamped on the other side thereby permitting convenient opening and closing of the mold. Of course, variations can be made in both continuous casting and closed-end mold casting methods to meet special requirements.

In the freezing of an ingot of an aluminum alloy in molds of the foregoing types, the aim is to produce a uniform progressive solidification, but in practice this is not always achieved. A non-uniform extraction of heat from the molten metal through the mold walls generally results in a variation in size of the grains and undissolved alloy constituents. This variation in constituent size as well as the distribution of the constituents is particularly evident in aluminum alloy ingots containing a substantial percentage of an insoluble element 'or elements such as iron, manganese and the like. Regions of an ingot where freezing occurs at a relatively slow rate generally contain relatively large segregated constituent particles whereas finer and more uniform distributed particles are found in those zones where solidification takes place at a relatively high rate. We have discovered that this variation in con-- stituent size and distribution, in ingots of aluminum-iron alloys, can be used to advantage if controlled, and carried over to products made from the ingots by providing a built-in decorative pattern on the surfaces of these products when they are properly subjected to a surface conversion treatment.

-It is therefore an object of the invention to impart an artistic pattern to surfaces of aluminum articles containing a substantial percentage of insoluble iron constituent that is of a permanent nature and therefore-suitable for use in architectural or other decorative applications.

Another object is to produce aluminum-iron alloy articles having alternating vertical bands of line and coarse particles of the aluminum-iron constituent, and to reveal such bands in the final product by a suitable surface treatment.

In accordance with the present invention, our new product, displaying a decorative pattern, is developed by casting an ingot of an alloy consisting essentially of aluminum and iron under such controlled non-uniform freezing conditions that intensify the variation in size of the aluminum-iron constituent to considerable depth below 'the 3,043,754 Patented July 10, 1962 c re ingot surface. The ingot thus cast comprises a shell of varying thickness of a matrix containing relatively large particles of aluminum-iron constituent enveloping a core composed of a matrix containing relatively small, finely divided particles of aluminum-iron alloy constituent. An undulating sharply defined boundary is formed between these two areas as a result of the I10n-unif0rm chilling of the metal.

The ingot so produced is then scalped or machined to such a depth as to remove any rough surface layer and into the zone of the undulating boundary thereby exposing alternating bands of the two metallurgical structures having sharp differences in particle size and distribution. The ingot prepared in this manner is then fabricated to the desired form by any of the well-known metal working processes, preferably by such elongating operations as rolling or extrusion. The surface of the fabricated product is subjected to a conversion treatment under such conditions as to reveal the pattern of alternate contrasting light and dark bands which closely resembles a marbleized pattern. The alternating streaks or hands are of varying length and width arising from the marked diiferences in form and distribution of the insoluble aluminumiron constituent and appear in shades of from very light to dark gray.

For a better understanding of our invention, reference is made herein to the accompanying figures where: I FIGURE 1 is a photograph, in actual size, of a typical plate made in accordance with our invention as described in greater detail in the example set forth below and revealing a pattern of contrasting light and dark areas;

FIGURE 2 is a photomicrograph, at a magnification of 500 diameters, of a typical section from the darker area of an ingot cast substantially as described in the example below, reflecting the presence of relatively small size particles of aluminum-iron constituent particles, and may be described as occurring in a eutectic like structure; and

FIGURE 3 is a photomicrograph at the same magnification of a section from the lighter area of the ingot associated with regions having relatively larger constituent particles which may be described as occurring in a non-eutectic like structure.

The attractive appearance of our product may be de scribed as the marbleized, varitoned, variegated, striated or wood grained patterns. It is significant that the pattern described above is inherent or built into the product, and consequently of a permanent nature. This is in contrast, for example, to the ordinary decorative aluminum surface made by dyeing or pigmenting an artificially-produced oxide coating.

The variation in constituent size is markedly exhibited in ingot castings of alloys consisting essentially of about 0.5 to 3% by weight iron, and preferably from about 1.5 to 2% by weight iron which closely approaches the eutectic composition of 1.8 to 1.9% iron, the balance being substantially aluminum. An iron content in excess of 3% results in the formation of too numerous primary particles of constituent which are relatively large as compared to the particles found in the eutectic, and therefore has an adverse effect on the contrast in pattern. Further, these primary particles result in weak spots in the product. 0n the other hand, an iron content below the described range results in poor contrast in the marbleized pattern.

We have found that up to about 0.5% by weight of silicon may be permitted without adversely affecting the contrast in pattern. Further, with regard to the insoluble elements, up to about 0.5% by weight of chromium, and about 0.1 to 1% each by weight of manganese, cobalt and nickel may be permitted or intentionally added to modify the desired pattern, but in no case should the total of these elements exceed 2%. Of the soluble elements, about 0.1 to 1% by weight magnesium and 0.1 to 5% by weight zinc may be permitted, and the copper content should not be more than about 2%, but the total of these elements should'notexceed more than about 5%. None of the foregoing elements, present Within the described ranges, obscure or mask the contrast in the pattern. However, the iron content preferably equals or exceeds the content of other elements.

Certain elements of thosenamed above may be employed to modify the tone of the marbleized pattern. For example, a bluish tone ma be imparted to the finished product by employing an aluminum-iron alloy containing 0.1 to 1% cobalt, and,*similarly, a gold tone by including 0.1 to 0.5% chromium in the alloy. 7 f

To develop the marbleized pattern, the aluminum-iron alloy is cast by one of the above-described methods of producing ingots under such freezing conditions as to accentuate the variation in constituent size. The direct chill :method of continuously casting aluminum base alloy ingots such as disclosed in United States Patent 2,301,027 to William T. Ennor, is especially suitable. In the Ennor patent, cooling of the ingot is accomplished by means of a water spray that floods a major portion of the mold shell by means of spray pipes surrounding the mold. The water jets impinge upon the outer surface of the mold and the water flows down over the embryoingot as it emerges below the mold. v

A variation in constituent size is attained to a particularly high degree by casting the ingot under such conditions that the freezing rate of the alloy is non-uniform, prefer: ably in both peripheral and longitudinaldirections. In the continuous casting and closed-end mold casting methods, non-uniform freezing conditions may be accomplished by subjecting the mold and ingot to a differential cooling action during the casting operation. For example, cyclic cooling of the ingot may be achieved by directing a water spray intermittently or in varying amountsraro-und performed at temperatures the periphery of the mold, or by directing the coolant .to

different portions of the mold. Other means for providing for a non-uniform extraction of heat from the molten metal during the casting operation'consists of attaching vertical strips of some light insulating material to portions of the exterior of the mold, or providing vertical grooves 4% below about 1000 F. will not substantially diminish this contrast in pattern. Therefore, the ingot can be rolled, forged or extruded according to most conventional practices. e

The variegated or marbleized pattern is fully developed upon a suitable conversion treatment'of the Worked aluminum alloy surface including the well known caustic etching and chemical and electro-cherm'cal coating methods. may be treated with a strong alkaline solution such as that of sodium hydroxide of preferably not less than 5% strength, or with a solution of an alkaline carbonate, for example a sodium carbonate-dichromate solution where the carbonate is usually not less than 2% and the dichro: mate not less than 0.1%. In the preferred method, the treatment is accomplished by the anodicoxidation of the aluminum. alloy surface whereby the aluminum is made the anode in a conventional electrolyte such as a 15% aqueous sulfuric acid solution, but it will be observed that the strength of the electrolyte, as Well as the current density, may be varied to satisfy the particular conditions. When, for example, a fabricated sheet of the aluminum-iron alloy is anodized, a marbleized pattern will appear because of the variation in constituent size. The light areas of the rolled sheet are associated with regions having a comparatively small number of relatively large particles of aluminum-iron constituent, while the dark areas reflect the presence of numerous but much smaller constituent par: ticles. These variations in-size'of the aluminnm iron constituent in'turn reflect Variations in the rate of chill.

of the molten metal during casting. Contrast in the marbleized pattern which may range from also black to a light gray metallic luster is also somewhat proportional to the thickness of the oxide coating produced, the thicker oxide coatings resulting in a greater contrast. To insure adequate protection and performance for outdoor application, however, the oxide coating should not be substantially thinner than about 0.8 mil.

Articles made in accordance with our invention are decorative in appearance, and are particularly useful in architectural applications such as metal'wall and door panels, pilasters, bars, display counters, and the like.

' Our invention is illustrated by the following example wherein an ingot 8 x30" x 60" having a nominal com position of 2% by weightiron and the balance aluminum The cast aluminum alloy ingot produced in the fore- M thereby exposing alternating bands of varying constituent size. In thescalping operation, any rough. surface layer condition, such as caused by exudation of lowmelting point constituents, is of course removed. Generally it is not necessary for the depth of the cut to exceed about 15% of the total thickness of the ingot, but scalping should be carried to a depth sutficient to expose alternating areas of constituent size. The ingot may be scalpe'd prior to any working operation, or, if preferred in rolling operations, scalping may be postponed until the ingot has been rolled to some intermediate thickness. The term ingot is therefore used to represent not only the as cast product but also a partially fabricated product such as abloom or billet.

Fabrication of the machined ingot should be carried out at a temperature below that which would tend to ,cause the relatively smaller constituent particles to increase or grow in size to the extent that a loss of contrast in pattern results. Generally, normal fabricating procedures and incidental impurities was cast at about 1330 to 1360 F. by the continuous direct chill method described above,

the mold having a jagged'bottom edge to increase non;

uniform chilling conditions. The cast ingot was scalped to a depth of A of an inch on each rolling surface, and then preheatedfor 14 hours at 925 F. The ingot was hot-rolled at 750 to 830 F. to 0.125 inch thick plate, and then cold rolled to 0.064 inch thick plate; The plate'was treated in a 5% sodium hydroxide solution at -150 F. to remove surface contaminants, and then anodized in a 15% sulfuric acid electrolyte for 50 to 60 minuteswith a current density of 12' amperes per square foot, the temperature of the electrolyte being 70 F. A decorative, marbleized pattern was exhibited on both surfaces of the plate, as shown in FIGURE 1. u Y

Specimens for FIGURES 2 and 3' were cut from an ingot cast substantially as described above and having the same nominal composition. These specimens which correspond to the light and dark areas obtained upon anodizing as above were polished, etched with Kellers etching solution, and photographed at a magnification of 500 diameters, according to standard practice.

Having thus described certain embodiments of our invention, we claim: V

1. A method of producing a wrought aluminum base alloy article having a permanently decorative pattern of by weight of iron under such non-uniform freezing conditions adjacent the periphery of the walls of the ingot as For example, the worked aluminum alloy surface to produce distinct zones having particles of aluminumiron constituent of substantially uniform size in each zone but the size of the particles in contiguous zones difiering sharply from each other, the said ingot comprising an outer shell of varying thickness containing relatively large particles of alminum-iron alloy constituent occurring in a substantially non-eutectic-like structure enveloping an inner core containing relatively small, finely divided particles of aluminum-iron alloy constituent occurring in a substantially eutectic-like structure, the boundary between said zones being distinct but undulatory and reflecting the non-uniform freezing conditions existing during formation of the said ingot, scalping at least one surface of the said ingot to such a depth as to cut transversely through the said undulating boundary thereby exposing alternating bands of diiferent sized particles of aluminumiron constituent, Working the said ingot in an axial direction at a temperature below that atiwhich the relatively small particles start to grow to form an elongated wrought product, and subjecting the surface of the said wrought product to an etching treatment to reveal the pattern. of contrasting light-and dark bands.

2. The method according to claim 1 wherein the said aluminum base alloy also contains 0.1 to 1% by weight of cobalt.

3. The method according to claim 1 wherein the said aluminum base alloy also contains 0.1 to 0.5% by weight of chromium.

4. The method according to claim 1 wherein the said aluminum base alloy also contains 0.1 to 1% by weight of magnesium.

5. The method according to claim 1 wherein the said aluminum base alloy also contains 0.1 to 1% by weight of nickel.

6. The method according to claim 1 wherein the said aluminum base alloy also contains 0.1 to 5% by weight of zinc.

7. A method of producing a wrought aluminum base -.a*lloy article having a permanently decorative pattern of contrasting light and dark bands on the surface thereof comprising casting an ingot of an aluminum base alloy 7 consisting essentially of aluminum and about 1.5 to 2% but the size-of the particles in contiguous zones differing sharply from each other, the said ingot comprising an outer shell of varying thickness containing relatively large particles of aluminum-iron alloy constituent occurring in a substantially non-eutectic-like structure enveloping an inner core containing relatively small, finely divided parholes of aluminum-iron alloy constituent occurring in a substantially eutectic-like structure, the boundary between said zones being distinct but undulatory and re fleeting the non-uniform freezing conditions existing dur ing formation of the said ingot, scalping at least one surface of the said ingot to such a depth as to cut'transversely through the said undulating boundary thereby exposing alternating bands of different sized particles of aluminumiron constituent, working the said ingot in an axial direction at a temperature below that at which the relatively smallparticles start to grow to form an elongated wrought product, and subjecting the surface of the said wrought product to an etching treatment to reveal the pattern of contrasting light and dark bands.

8. As an article of manufacture, a Wrought aluminum base alloy product consisting essentially of aluminum and about 0.5 to 3% by weight of iron, said article having an etched surface and a built-in pattern of contrasting light and dark elongated bands, said dark bands being characterized by the predominance of relatively small, finely divided particles of aluminum-iron alloy constituent occurring in a substantially eutectic-like structure and said light bands being characterized by the predominance of relatively large particles of aluminum-iron alloy constitu' ent occurring in a substantially non-eutectic-like strucwife.

9. The method according to claim 1 wherein the electro-chemical etching treatment includes anodic oxidation of the surface.

10. The article according to claim 8 wherein the etched surface is covered with an anodically produced oxide film.

11. The article according to claim 8 wherein the aluminum base alloy also contains at least one of the elements of the group composed of 0.1 to 0.5% chromium, 0.1 to

1% manganese, 0.1 to 1% cobalt and 0.1 to 1% nickel,

the total amount of said elements not exceeding 2% a 12. The article according to claim 8 wherein the aluminum base alloy also contains from 0.1 to 1% magnesium. 13. The article according to claim 8 wherein the alumi num base alloy also contains from 0.1 to 5% zinc;

14. The article according to claim 8 wherein the aluminum base alloy also contains up to 2% copper.

References Cited in the file of this patent UNITED STATES PATENTS Mostovych et al. June 21, 1960 OTHER" REFERENCES Metals Handbook, 1948 edition, published by American Society for Metals, Photomicrog-raphy by I. R. Vilella, page 162. I

Metals Handbook, 1948 edition, published by American Society for Metals, page 770. 

1. A METHOD OF PRODUCING A WROUGHT ALUMINUM BASE ALLOY ARTICLE HAVING A PERMANENTLY DECORATIVE PATTERN OF CONTRASTING LIGHT AND DARK BANDS ON THE SURFACE THEREOF COMPRISING CASTING AN INGOT OF AN ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF ALUMINUM AND ABOUT 0.5 TO 3% BY WEIGHT OF IRON UNDER SUCH NON-UNIFORM FREEZING CONDITIONS ADJACENT THE PERIPHERY OF THE WALLS OF THE INGOT AS TO PRODUCE DISTINCT ZONES HAVING PARTICLES OF ALUMINUMIRON CONSTITUENT OF SUBSTANTIALLY UNIFORM SIZE EACH ZONE BUT THE SIZE OF THE PARTICLES IN CONTIGUOUS ZONES DIFFERING SHARPLY FROM EACH OTHER, THE SAID INGOT COMPRISING AN OUTER SHELL OF VARYING THICKNESS CONTAINING RELATIVELY LARGE PARTICLES OF ALUMINUM-IRON ALLOY CONSTITUENT OCCURRING IN A SUBSTANTIALLY NON-EUTECTIC-LIKE STRUCTURE ENVELOPING AN INNER CORE CONTAINING RELATIVELY SMALL, FINELY DIVIDED PARTICLES OF ALUMINUM-IRON ALLOY CONSTITUENT OCCURING IN A SUBSTANTIALLY EUTECTIC-LIKE STRUCTURE, THE BOUNDARY BETWEEN SAID ZONES, BEING DISTINCT BUT UNDULATORY AND REFLECING THE NON-UNIFORM FREEZING CONDITIONS EXISTING DURING FORMATION OF THE SAID INGOT, SCALPING AT LEAST ONE SURFACE OF THE SAID INGOT TO SUCH A DEPTH AS TO CUT TRANSVERSELY THROUGH THE SAID UNDULATING BOUNDARY THEREBY EXPOSING ALTERNATING BANDS OF DIFFERENT SIZED PARTICLES OF ALUMINUMIRON CONSTITUENT, WORKING THE SAID INGOT IN AN AXIAL DIRECTION AT A TEMPERATURE BELOW THAT AT WHICH THE RELATIVELY SMALL PARTICLES START TO GROW TO FORM AN ELONGATED WROUGHT PRODUCT, AND SUBJECTING THE SURFACE OF THE SAID WROUGHT PRODUCT TO AN ETCHING TREATMENT TO REVEAL THE PATTERN OF CONTRASTING LIGHT AND DARK BANDS. 